[CQ-Contest] oxidized inner conductor when coax carries DC power

Jim Brown k9yc at audiosystemsgroup.com
Mon Oct 31 21:38:23 EDT 2016

Hi Franki,

I would not be so sure that it is not moisture.  A few years ago, I 
replaced a center insulator on one of my high dipoles with one that my 
neighbor had built. Less than a year later, I noticed moisture at the 
SO239 on the panel where that feedline is grounded. I opened up the coax 
and found the braid almost solid black. The entry point for the water 
was at the new insulator, and it flowed all the way down the coax. I 
later confirmed that when I replaced the coax and cut it at the top. 
That dipole is up 140 ft, so the water flowed 160 ft down to the shack 
entry point.  The coax was Belden 8213, which has a foam dielectric and 
a heavy copper braid shield.

I don't recall whether the center conductor was also black or not, but 
the center conductor is molded to the dielectric, so I suspect it was not.

73, Jim K9YC

On Mon,10/31/2016 3:51 AM, Franki ON5ZO wrote:
> Much to my surprise I found the inner conductor black from corrosion. 
> I cut off a few centimeters at a time, but after having cut off two 
> meters, it still was black. I have been working with these things for 
> ages and I can tell you: it is NOT water ingress. 

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